Such a device is known from EP-A-345 874 which corresponds substantially to U.S. Pat. No. 4,927,228. In this known device, the two holders and the intermediate piece are adjustable relative to one another both in axial and in transversal direction, while the use of laser welds on thinned portions leads to a fastening which exerts hardly any thermal and mechanical forces and thus does not cause any gradual mis-alignment. In the embodiment shown in FIG. 3 of EP-A-345 874, in which a lens is used, this lens has a rod-shape and is included in the intermediate piece. The holder for the semiconductor laser diode is shaped as a sleeve here, in which the envelope of the semiconductor laser diode is accommodated. This sleeve is axially adjustable relative to the intermediate piece. The lens is aligned relative to the semiconductor laser diode in this case. The end of the optical transmission fiber is set at a fixed distance from the lens in an adaptor.
This arrangement gives a sufficient accuracy for obtaining a good coupling efficiency for a multimode optical transmission fiber. In the case of a single-mode optical transmission fiber, however, it is difficult to obtain in a reproducible manner the desired alignment accuracy and stability with this device.